A chain tensioner device applies tension to a drive chain moving at a high speed by pressing a chain guide against some intermediate point of the drive chain looped around drive and driven sprockets, in a direction substantially perpendicular to a direction of travel of the chain. Referring to FIG. 33, the constitution of a valve operating system of an engine will be described below.
FIG. 33 shows a front view of the constitution of a valve operating system in an engine. As illustrated in FIG. 33, a cylinder head 103 is provided on top of a cylinder block 102 of an engine 101.
A crankshaft 105 is rotatably provided in the cylinder block 102, and a crankshaft sprocket 106 is fixed to the end of the crankshaft 105. The cylinder head 103 is provided with an idle sprocket 107. A timing chain 140 is looped around the idle sprocket 107 and the crankshaft sprocket 106.
A small sprocket 109 is coaxially provided for the idle sprocket 107. A cam chain 112 is looped around this sprocket 109 and camshaft sprockets 111, 111 fixed to two, left and right camshafts 110, 110 of the cylinder head 103.
In this constitution, the crankshaft 105 drives the left and right camshaft sprockets 111, 111 and the camshafts 110, 110 in the cylinder head 103 by means of the crankshaft sprocket 106, the timing chain 140, the idle sprocket 107 and the cam chain 112.
It is noted that in FIG. 33, the timing chain 140 rotates clockwise.
A given tension is always applied to the timing chain 140 by a chain guide 120 and a chain tensioner 114 for the timing chain 140. In addition, the timing chain 140 is hampered from swinging by means of a guide 117 provided on a side of the timing chain 140.
The chain guide 120 for the timing chain 140 is of a curved shape, where the sliding surface at the convex curved side is pressed against the timing chain 140 by the chain tensioner 114 being activated by hydraulic pressure, thereby preventing the timing chain 140 from loosening.
The chain guide 120 for the timing chain 140 sustains a considerably large pressing force, which forces the timing chain 140 to rotate against sliding resistance stemming from friction between the timing chain 140 and the chain guide 120.
At that time, the sliding resistance generated by the friction between the chain guide and the drive chain disadvantageously increases noise and mechanical loss.
As an approach to reduce such noise and mechanical loss, the technique disclosed in Patent Literature 1 is known. A chain tensioner device as described in Patent Literature 1 is provided for a valve operating system of an engine to apply tension to a timing chain. The device has rollers disposed on the sliding surface contacting with a timing chain in a curved chain guide, and the rollers are rolling-pressed against the timing chain moving in its longitudinal direction at a high speed to reduce sliding resistance.
However, the aforementioned chain tensioner device as disclosed in Patent Literature 1 still involves the following drawback. That is, because the rollers are mounted on the chain guide by way of sliding bearings, revolution of the rollers entails sliding friction. Moreover, because the rollers disposed on the chain guide press the timing chain with a large pressing force, sliding friction between the rollers and the chain guide increases, which still causes mechanical loss.
In the above-mentioned chain tensioner device as described in Patent Literature 1, the rollers are secured on the chain guide by inserting screws through the sides of the chain guide and fastening the screws with nuts.
Such a conventional chain tensioner device thus utilizes a plurality of components, such as screws and nuts, to fasten the rollers to the chain guide, which presents a drawback that an increased number of components and cost are required as well as assembling efficiency is lowered.
There is another drawback that although strength and weight reduction are requisites for automotive parts, an increase in the number of components is inconsistent with the weight reduction.